1. Field of the Invention
The present invention relates to a technique of correcting an image blur due to a shake of an image capturing apparatus.
2. Description of the Related Art
Conventionally, an image stabilization function detects a shake of an apparatus, and moves an image stabilization member (an image stabilization lens and a holding member therefor), which is movable to correct an image blur due to the detected shake, in a direction to cancel a shake amount.
On the other hand, there has been conventionally proposed an image capturing apparatus which uses a so-called pixel shifting technique. In this technique, a plurality of sets of image signals are obtained by performing shooting a plurality of times while slightly changing the relative position between an object image formed by an imaging optical system and an image sensor for photoelectrically converting the object image, and are combined by a predetermined method, thereby obtaining a high-resolution image. For example, the following related art literatures for the pixel shifting technique are well known.
In Japanese Patent Laid-Open No. 7-287268, a variable angle prism in front of an imaging optical system is driven based on an image blur signal and pixel shifting signal to parallelly decenter an optical image on an image sensor, thereby cancelling an image blur by image stabilization and obtaining a high-resolution image by pixel shifting at the same time. This literature also discloses to prohibit pixel shifting control when the focal length of the imaging optical system is equal to or larger than a predetermined value.
In addition, Japanese Patent Laid-Open No. 10-191135 discloses a technique of changing an operation of, for example, changing the number of times pixel shifting is performed, in accordance with the setting state of an exposure control condition setting unit for deciding, as an image capturing condition, the combination of an f-number and exposure time.
The methods described in Japanese Patent Laid-Open Nos. 7-287268 and 10-191135 have a high driving accuracy of an image stabilization member for pixel shifting under a specific ideal condition, and are proven to be effective. The specific ideal condition indicates that no large shake acts on an image capturing apparatus and thus no acceleration disturbance is caused, or that the influence such as static friction is very small in driving of the image stabilization member and thus the tracking accuracy of the image stabilization member for a pixel shifting command is high.
In fact, however, there is static friction to some extent at the driving unit of the image stabilization member. Since a command position for pixel shifting is driven by a small amount such as 1 or 0.5 pixel of the image sensor, it is readily influenced by friction, and thus it is difficult to perform pixel shifting by a correct distance. To solve this problem, it is necessary to attain a mechanical driving characteristic of the image stabilization member which receives little influence of friction and has a high driving accuracy so as to cope with driving of pixel shifting, which may increase the cost.
Furthermore, if a step command signal is sent to the image stabilization member for pixel shifting, an overshoot or deviation in tracking position of the image stabilization member may occur. In this case, a delay occurs until the target position (1 or 0.5 pixel) of pixel shifting is reached, thereby delaying exposure processing.